Method and device for monitoring platelet function

ABSTRACT

The invention provides a method of monitoring platelet function in a mammal by passing blood removed from the body of the mammal through a passageway to contact an obstruction or irregularity in the passageway to generate a platelet mass in the passageway, and monitoring the flow or composition of the blood in the passageway to detect the platelet mass. The flow and composition change in response to the formation of a platelet mass in the passageway. Devices, articles, and kits for performing the methods are also disclosed.

BACKGROUND

Platelets are anucleated cells that are the primary cells responsiblefor stopping bleeding. Blood platelets are approximately 3 microns insize and circulate in the blood stream as disc shaped cells that uponactivation by either tissue injury or exposure to a foreign materialundergo physiological changes that lead to aggregate formation at thesite of injury or foreign material. Blood platelets circulate atapproximately 250,000 to 350,000 platelets per microliter of wholeblood. Upon activation, platelets change shape from a disc to a sphereand form pseudopodia elongations.

The normal platelet response to initiate cessation of bleeding is toundergo a shape change, attach to the surface, and release intraplateletcomponents that act to provide an autocatalytic recruitment of moreplatelets. With the recruitment of additional platelets, a platelet plugor aggregate mass forms. The aggregate mass evolves from a singleplatelet of only 3 microns in size to a mass on the order of millimetersin size. The platelet mass additionally recruits and participates withthe plasma coagulation proteins. The plasma coagulation proteins undergoa cascade of events involving 13 enzymes and cofactors, which leads tothe activation of plasma fibrin to form a fibrin clot.

It is useful here to briefly summarize the biochemical events ofhemostasis (the cessation of bleeding). Normal intact endothelium doesnot initiate or support platelet adhesion (although in certain vasculardiseases platelets may adhere to intact endothelium). Vascular injury,however, exposes the endothelial surface and underlying collagen.Following vascular injury, platelets attach to adhesive proteins such ascollagen via specific glycoproteins on the platelet surface. Thisadhesion is followed or accompanied by platelet activation, whereplatelets undergo a shape change from a disc shape to a spherical shapewith extended pseudopodia. At this time, the platelet release reactionalso occurs. The platelets release biologically active compounds storedin the cytoplasmic bodies that stimulate platelet activation or areotherwise involved in clotting reactions. These include ADP, serotonin,thromboxane A₂, and von Willebrand factor. Thromboxane A₂ is a potentinducer of platelet secretion and aggregation. It is formed by theenzyme cyclooxygenase, which is inhibited by aspirin, among other drugs.

Following activation, glycoprotein IIb and IIIa (GPIIbIIIa) receptors onthe surface of the platelets undergo a conformational change from arelatively inactive conformation to an activated form. GPIIbIIIareceptors mediate the adhesion of more platelets by adhering to thecirculating plasma protein fibrinogen, which serves as a bridging ligandbetween platelets. The adhesion and aggregation of platelets constitutesprimary hemostasis.

Secondary hemostasis stabilizes the platelet mass by forming a fibrinclot. The fibrin clot is the end product of a series of reactionsinvolving plasma proteins. The process is known as blood coagulation.Among the plasma proteins involved are the activated forms of theclotting factors II, VII, IX, X, XI, and XII (the activated forms havean “a” following the Roman numeral, e.g., factor IIa). The activatedforms of these proteins are serine proteases.

Fibrin is formed from fibrinogen, a large circulating plasma protein, byspecific proteolysis. In the process, the protein thrombin (factor IIa)is consumed. Fibrin monomers next spontaneously associate to formpolymers and form a loose reinforcement of the platelet plug. Fibrinpolymers are then cross-linked by certain enzymes. The fibrin polymeralso traps red cells and white cells to form a finished clot.

Under normal conditions of hemostasis, the individual experiencingbleeding benefits from the ability of platelets to change shape, adhere,spread, release chemical messengers and activators, aggregate, andassemble with fibrin. This series of events stops bleeding at the siteof injury and initiates the process of wound healing.

But platelet activation and clot formation can also place a person atrisk of pathological cardiovascular events. For example, venous bloodclot formation in the legs, a condition known as deep vein thrombosis,creates the risk that the blood clots could embolize (break apart) andresult in clot entrapment in the lungs or the brain, causing pulmonaryembolisms and stroke-related conditions. Platelet activation and fibrinformation in other locations in some persons create aggregates and smallclots in the arterial circulation that can also lead to embolization andstrokes.

In addition to age and genetic and lifestyle risk factors, implantedmedical devices in the blood stream also place patients at greater riskof clot formation and embolization. Each year, approximately 500,000heart valves are implanted in the United States. Although biomaterialadvancement has somewhat reduced the risk of thrombosis (clotformation), all patients with mechanical heart valves are at increasedrisk of clot formation, embolization, and stroke.

Arterial stents are another type of device placed in the circulatorysystem that place patients at risk from platelet activation. Arterialstents are placed in clogged coronary and carotid arteries to provideoxygen to cardiac tissue. They are typically around 5 mm in diameter andare made from stainless steel or other materials. Due to theintroduction of a foreign material in the blood stream, platelets canbecome activated and attach to the wall of the stented vessel. Thisleads to reocclusion (restenosis) of the stented vessel, which is a verysignificant risk in patients with arterial stents. Restenosis in thefirst 28 days is reported in 0.5 to 8% of persons receiving stents.

In an effort to reduce the risk of embolization and restenosis, patientsreceiving heart valves or arterial stents are commonly placed onanti-coagulant or platelet-inhibiting medications before, during, andafter the procedures.

Current platelet inhibiting drugs fall into three groups: (1)aspirin-related drugs, which inhibit the platelet cyclooxygenase enzyme,thus reducing production of thromboxane A₂, which is a plateletactivator; (2) ADP-receptor inhibiting drugs, which block a surfacemembrane receptor on the platelets that is involved in the activationprocess; (3) monoclonal antibodies that block GPIIbIIIa receptors on theplatelet surface. The GPIIbIIIa receptor binds the plasma coagulationfactor fibrinogen, which is involved in both aggregation and in forminga fibrin clot.

All three approaches are effective in reducing platelet activation,however no intervention is successful on all patients. Aspirin is theleast expensive. But the appropriate dose varies unpredictably fromperson to person, and up to 30% of individuals on long-term aspirintherapy do not achieve inhibition of platelet adhesion. TheADP-inhibiting drugs are more expensive than aspirin, but are gainingpopularity. However, as with aspirin, the required dose and duration oftherapy varies, and a large variation in platelet adhesioncharacteristics in patients on the drugs exists. TheGPIIbIIIa-inhibiting drugs are argued to provide the greatest plateletinhibition, but they are very expensive and still suffer frompatient-to-patient variability in dosing and effectiveness. Othermedications are likely to emerge, but all will probably still have thepatient-to-patient variability seen with other approaches.

The failure to determine the proper dose and medication to inhibitplatelets can have a great cost in money, and can cause unnecessarymorbidity and death. For example, patients on anti-GPIIbIIIa drugs havebeen reported to have from a 5.8 to 11.2% incidence of adverse reactionsin the first 28 days after stenting. The adverse reactions were definedas death, myocardial infarction, or urgent need for reintervention withangioplasty procedures. The risk was even higher when patients were nottreated with the drugs. (New England J. Med. 330:956-961, 1994; New.England J. Med. 336:1689-96A, 1997; Lancet 349:1429-35, 1997.)

Thus, anti-platelet drugs have a large patient-to-patient variabilityand many patients are refractory to some anti-platelet drugs. A methodis needed to monitor platelet function so the proper dose of ananti-platelet drug for a particular patient can be determined, and so aphysician can determine whether a particular patient is refractory toone anti-platelet drug but responsive to another.

No reliable point-of-care method currently exists to specificallydetermine if platelet adhesion and aggregation have been inhibited.Thus, there is a need for a method and a device to measure plateletfunction, and preferably to measure platelet adhesion and aggregation aspart of the measurement of platelet function. The need to measureplatelet function is particularly acute in patients receiving arterialstents or other cardiovascular devices, and in other persons at risk ofadverse cardiovascular events. Such a method would allow an attendingphysician to ensure that platelet function has in fact been inhibited ina patient at risk, and to adjust pharmacologic parameters prior toimplanting a cardiovascular device, which will reduce the risk ofadverse events associated with platelet initiation of clot formation.

Another need to monitor platelet function arises in platelettransfusions. Platelets are harvested and used in platelet transfusionsto support patients at risk of bleeding. However, platelet storage posesproblems not found with the storage of whole blood or other components.Whole blood, red and white cells may be stored at 4° C. for weeks.However, platelets will aggregate in cold storage and when allowed tosettle. Therefore, the standard means of storing platelets is at roomtemperature with gentle agitation. Even under these conditions,platelets lose function by about 5 days. Thus, methods and devices formonitoring platelet function are also needed to determine whether storedplatelets have adequate activity to be transfused into patients.

Another need to monitor platelet function exists to test patientsundergoing a medical or dental procedure for their risk of excessivebleeding during the procedure.

Accordingly, a need exists for a method to measure platelet function.Preferably, the method would monitor platelet adhesion and aggregation.Preferably, the method would monitor platelet function specifically,separately from the other aspects of clotting such as blood coagulation.Preferably, the method would be inexpensive. Preferably, the methodwould not depend upon platelet activation by any particular chemicalplatelet activator or group of chemical platelet activators. Preferably,the method could be used on whole, unprocessed blood, and could produceresults quickly (e.g., be used at the bedside, during a physician visit,or during a medical procedure to provide a result almost immediately).Devices to monitor platelet function are also needed.

SUMMARY OF THE INVENTION

The invention provides methods and devices for assessing plateletfunction, as evidenced by platelet adhesion, and preferably plateletaggregation. In the methods, blood is drawn through a passageway, suchas a catheter, past or against an obstruction or irregularity in thepassageway, such as a wire placed in the catheter. The platelets adhereand aggregate on the obstruction or on the wall of the passageway nearthe obstruction or irregularity, and form a platelet mass. It isbelieved that shear forces associated with passing or contacting theobstruction or irregularity in the passageway activate the platelets andinduce them to adhere to the foreign material of the obstruction or thewalls of passageway and to aggregate. When the plug forms, it occludesthe lumen of the passageway and flow stops or slows. The time of partialor full occlusion of the lumen can be recorded as the platelet plugformation time.

Since a plug is the end product of platelet activity, formation of aplug depends on the functioning of all platelet activities, includingplatelet adhesion and, if the plug is thicker than about 15 microns,platelet aggregation. (If the plug is thicker than about 15 microns, itinvolves more than a layer of platelets that forms due to plateletadhesion to a surface, but rather involves a mass formed byplatelet-to-platelet aggregation.) This contrasts with some currentplatelet tests that measure only one specific platelet activity, such asrelease of a particular biochemical, or depend only on platelet adhesionand not aggregation. It has been found that the platelet mass in themethods of the present invention contains little or no fibrin or red orwhite blood cells. Thus, in at least some embodiments, the methods ofthe invention measure platelet function specifically, independently ofthe blood coagulation reactions.

No chemical or biological platelet activators need to be added to theblood or the passageway for the present methods, although in someembodiments they optionally can be added. Thus, the methods do notdepend on platelets responding to a particular biochemical activator orparticular group of activators. The methods are fast and can use wholeunprocessed blood. Accordingly, they can produce results quickly andinexpensively with a small sample of blood taken at the patient'sbedside, during a physician visit, or during an interventionalprocedure.

Thus, the invention provides a method of monitoring platelet functioncomprising: passing blood removed from a mammal through a passagewaycomprising an obstruction or an irregularity, to contact the obstructionor the wall of the passageway at the irregularity, to generate aplatelet mass in the passageway; and monitoring the flow or compositionof the blood in the passageway to detect formation of the platelet mass;wherein the passageway does not comprise an added biological agent thatactivates platelets.

The invention also provides a method of monitoring platelet function ina mammal comprising: passing blood removed from a mammal through apassageway comprising an obstruction or an irregularity, to contact theobstruction or the wall of the passageway at the irregularity, togenerate a platelet mass in the passageway; and monitoring the flow orcomposition of the blood in the passageway to detect formation of theplatelet mass; wherein the platelet mass is substantially depleted infibrin in comparison to a natural clot.

The invention further provides a device for monitoring plateletfunction, comprising: (a) a fluid-tight material forming a passageway;(b) a pump functionally linked to the passageway for pumping bloodthrough the passageway; (c) an obstruction within the passageway,arranged such that when blood is pumped through the passageway tocontact the obstruction, a platelet mass substantially free of fibrinforms on or near the obstruction; and (d) a means for detecting the flowof blood through the passageway to detect formation of the plateletmass.

The invention further provides a device for monitoring plateletfunction, comprising: (a) a fluid-tight material forming a passageway;(b) a pump functionally linked to the passageway for pumping bloodthrough the passageway; (c) an obstruction within the passageway,arranged such that when blood is pumped through the passageway tocontact the obstruction, a platelet mass substantially free of fibrinforms on or near the obstruction; and (d) a means for detecting thecomposition of blood in the passageway to detect formation of theplatelet mass.

The invention also provides a device for monitoring platelet function,comprising: (a) a fluid-tight material forming a passageway; (b) a pumpfunctionally linked to the passageway for pumping blood through thepassageway; wherein the passageway comprises an irregularity arrangedsuch that when blood is pumped through the passageway to contact thewall of the passageway at the irregularity, a platelet masssubstantially free of fibrin forms on the wall of the passageway at ornear the irregularity; and (c) a means for detecting the flow of bloodthrough the passageway to detect formation of the platelet mass.

The invention also provides a device for monitoring platelet function,comprising: (a) a fluid-tight material forming a passageway; (b) a pumpfunctionally linked to the passageway for pumping blood through thepassageway; wherein the passageway comprises an irregularity arrangedsuch that when blood is pumped through the passageway to contact thewall of the passageway at the irregularity, a platelet masssubstantially free of fibrin forms on the wall of the passageway at ornear the irregularity; and (c) a means for detecting the composition ofblood in the passageway to detect formation of the platelet mass.

The invention further provides a device for monitoring plateletfunction, comprising: (a) a fluid-tight material forming a passageway;(b) a pump functionally linked to the passageway for pumping bloodthrough the passageway; (c) an obstruction within the passageway,arranged such that when blood is pumped through the passageway tocontact the obstruction, a platelet mass substantially free of fibrinforms on or near the obstruction; and (d) a blood flow detector todetect formation of the platelet mass.

The invention further provides a device for monitoring plateletfunction, comprising: (a) a fluid-tight material forming a passageway;(b) a pump functionally linked to the passageway for pumping bloodthrough the passageway; (c) an obstruction within the passageway,arranged such that when blood is pumped through the passageway tocontact the obstruction, a platelet mass substantially free of fibrinforms on or near the obstruction; and (d) a blood composition detectorto detect formation of the platelet mass.

The invention also provides a device for monitoring platelet function,comprising: (a) a fluid-tight material forming a passageway; (b) a pumpfunctionally linked to the passageway for pumping blood through thepassageway; wherein the passageway comprises an irregularity arrangedsuch that when blood is pumped through the passageway to contact thewall of the passageway at the irregularity, a platelet masssubstantially free of fibrin forms on the wall of the passageway at ornear the irregularity; and (c) a blood flow detector to detect formationof the platelet mass.

The invention also provides a device for monitoring platelet function,comprising: (a) a fluid-tight material forming a passageway; (b) a pumpfunctionally linked to the passageway for pumping blood through thepassageway; wherein the passageway comprises an irregularity arrangedsuch that when blood is pumped through the passageway to contact thewall of the passageway at the irregularity, a platelet masssubstantially free of fibrin forms on the wall of the passageway at ornear the irregularity; and (c) a blood composition detector to detectformation of the platelet mass.

The invention also provides an article for use in a device formonitoring platelet function, the article comprising: a fluid-tightmaterial forming a passageway; and an obstruction in the passageway,arranged such that when blood is pumped through the passageway tocontact the obstruction, a platelet mass substantially free of fibrinforms on or near the obstruction.

The invention also provides an article for use in a device formonitoring platelet function, comprising: a fluid-tight material forminga passageway; wherein the passageway comprises an irregularity arrangedsuch that when blood is pumped through the passageway to contact thewall of the passageway at the irregularity, a platelet masssubstantially free of fibrin forms on the wall of the passageway at ornear the irregularity.

The invention also provides a kit for use in monitoring plateletfunction, comprising packaging material containing: (a) an articlecomprising: (i) a fluid-tight material forming a passageway; and (ii) anobstruction in the passageway, arranged such that when blood is pumpedthrough the passageway to contact the obstruction, a platelet masssubstantially free of fibrin forms on or near the obstruction; and (b)instruction means indicating the article is to be used in a device formonitoring platelet function.

The invention also provides a kit for use in monitoring plateletfunction, comprising packaging material containing: (a) an articlecomprising: a fluid-tight material forming a passageway; wherein thepassageway comprises an irregularity arranged such that when blood ispumped through the passageway past the irregularity, a platelet masssubstantially free of fibrin forms on the wall of the passageway at ornear the irregularity; and (b) instruction means indicating the articleis to be used in a device for monitoring platelet function.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-G show passageways for the passage of blood, with various typesof obstructions and irregularities in the passageways.

FIG. 2 is a schematic drawing of a device of the invention.

DETAILED DESCRIPTION Definitions

“Platelet function” refers to platelets adhering to a substrate,changing shape, releasing chemical messengers or clotting factors storedin the cytoplasm of the platelets, and/or aggregating with otherplatelets. “A biological or chemical agent that activates platelets”refers to a substance that upon contact with platelets induces plateletsto perform any of those platelet functions (without a requirement thatthe platelets be exposed to shear or any other mechanical activator).

The term “a biological agent that activates platelets” refers to anagent found naturally in a mammalian body that has the biological roleof activating platelets, such as collagen, ADP, thrombin, thromboxaneA₂, serotonin, and epinephrine.

“A chemical agent that activates platelets” refers to a compound thatactivates platelets other than a mammalian biological agent. Itincludes, e.g., non-biological synthetic compounds, derivatives ofbiological agents that activate platelets, or biological agents found inplants or microorganisms that activate platelets.

“An added biological or chemical agent” refers to a compound orsubstance that is added to the blood after removal from the body. An“added agent in the passageway” refers to an agent placed orincorporated in the passageway prior to addition of blood to thepassageway. The agent could be, for instance, adhered to the wall of thepassageway or to an obstruction in the passageway.

“Obstruction” refers to an object that partially or fully obstructs thepassageway. Preferably the obstruction partially obstructs thepassageway. Examples of obstructions include (a) a plug, such as a wire,that occupies a portion of the passageway (preferably with a spacebetween the plug and the wall of the passageway), (b) a filter or mesh,or (c) a fiber.

As used herein, an obstruction in the passageway that is a “plug” is asolid nonporous object that partially or fully obstructs the passageway.The plug can be any shape in cross-section, e.g., circular, square, orrectangular, and can be composed of any non-porous material, e.g.,plastic or metal.

“Blood” as used herein refers to whole blood or to a blood fractioncontaining platelets. Preferably, blood is removed from the mammal andthen passed through the passageway in the methods of the inventionwithout any processing and without the addition of any agents (e.g.,anti-coagulants or platelet activators). However, the method will alsowork with purified platelets or with any blood fraction enriched inplatelets or containing platelets. Accordingly, the term “blood”includes platelet-containing plasma, purified platelets, or any bloodfraction containing platelets.

The term “whole blood” refers to blood that has not been fractionated.

A “platelet mass” as used herein refers to any mass that ispredominantly platelets. The mass can also contain fibrin and othercells. Preferably, it is depleted in fibrin and depleted in other cellsas compared to a natural clot. A platelet mass can be less than about 15microns thick in one or more dimensions, i.e., consisting of a layer ofplatelets about 5 or fewer platelets thick and formed by plateletadhesion, with little or no platelet-to-platelet aggregation.Preferably, however, the platelet mass is thicker than about 15 micronsin all dimensions. The term “platelet plug” is used interchangeably with“platelet mass.”

DESCRIPTION

The invention provides a method of monitoring platelet function in amammal involving passing blood removed from the body of the mammalthrough a passageway to contact an obstruction or irregularity in thepassageway to generate a platelet mass in the passageway, and monitoringthe flow or composition of blood in the passageway. The formation of aplatelet mass causes a change in the flow or composition of the blood inthe passageway, and the change in flow or composition is detected.

In devices of the invention, blood passes through a passageway 100,formed by fluid-tight walls 110 of a foreign material (i.e., anymaterial other than the endothelium of a natural blood vessel). (FIG.1A). Preferably, the foreign material is a non-biological material. Itcan be, for instance, any type of plastic, glass, rubber, TEFLON, ormetal. Within the passageway is an obstruction or irregularity. Apassageway with obstruction 120 is shown in FIG. 1A. The obstruction isalso preferably made of a foreign material. It can be porous ornon-porous. It can be the same material as the wall of the passageway ora different material.

Blood is pumped through the passageway to contact the obstruction or thewall of the passageway at the irregularity. The obstruction orirregularity creates areas of high shear and low shear for fluidspassing through the passageway. It is believed that high shear activatesthe platelets and areas of low shear allow the platelets to adhere andform a platelet mass. Preferably, the blood is pumped past theobstruction or irregularity, until a platelet mass forms that preventsor resists blood passing. However, the obstruction can totally occludethe passageway, and the irregularity can be a closed end of thepassageway, where blood can not pass the obstruction or irregularity. Inthat case, blood can be passed back and forth against the occludingobstruction or irregularity until a platelet mass forms that isdetected.

One example of an obstruction is a wire 120 as shown in FIG. 1A. Theobstruction preferably only partially obstructs the passageway.Preferably the obstruction leaves a gap of at least about 20 micronsbetween the obstruction and the passageway wall. Thus, in that case, inorder to fully occlude the passageway the platelet mass must be at leastabout 20 microns thick. To form a mass that size, the platelets must notmerely adhere to the surface but must also aggregate to each other.Thus, in this embodiment the method tests the ability of the plateletsto show both the activity of adhering and the activity of aggregating.

As blood is pumped past the obstruction 120, a platelet mass is formedon or near the obstruction. Typically, the platelet mass forms at alocation of low shear, such as on the end of a wire obstruction.Platelet function can be monitored by measuring the time until partialor full occlusion of the passageway. Occlusion of the passageway can bedetected by any suitable means. For instance, a light-emitting diode anda coupled detector can be placed across one point of the passageway todetect passing of the red blood past that point. A pressure transducercan be used to monitor the pressure needed to pump the blood. Thepassageway can be placed across the light path of a spectrophotometer,so that the spectrophotometer detects (a) the passing of red blood pastthe light path, (b) an increase in scattering and/or a change in colorat the point of the platelet plug as the platelet plug develops, if thelight path is positioned to pass through the expected point where theplatelet plug forms, or (c) a change in color of the blood outside ofthe platelet plug associated with the formation of the platelet plug.The time it takes the blood to pass from point A to point B can bemeasured. Chemical sensors can also be used to measure theconcentrations of particular biochemicals that change, either in theblood as a whole or in microenvironments at or near the platelet mass,as the platelet mass forms. For instance, pH, Mg⁺⁺ concentration, K⁺concentration, Na⁺ concentration, O₂ concentration, or CO₂ concentrationcan be monitored by sensors and methods known in the art.

The dimensions of the passageway and obstruction or irregularity can beany dimensions suitable, i.e., wide enough to allow blood to pass freelythrough the passageway until a platelet mass forms, and narrow enoughthat upon formation of a platelet mass the occlusion of the passagewaycan be detected. For instance, the passageway can be a millimeter orless in diameter or more than a cm in diameter. A wire obstruction ofthe passageway can leave, for instance, a gap of about 50 microns withthe passageway wall. Other larger and smaller gap sizes and dimensionsare also possible.

Blood can be pumped bidirectionally or unidirectionally through thepassageway. Pumping the blood bidirectionally, i.e., back and forth pastthe obstruction or irregularity, has the advantage that it allows asmaller volume of blood to be used. Also, with bidirectional flow, anyplatelet mass formation time can be measured with a finite amount ofblood. With unidirectional flow of blood through a linear passagewaythat is open at both ends, longer platelet mass formation times willrequire the use of more blood.

Pumping blood unidirectionally through a closed loop, where the bloodcan cycle the loop as many times as necessary, has the same advantagesas bidirectional flow, namely allowing the use of smaller volumes ofblood and allowing measurement of extended plug formation times.

Thus, some embodiments of the devices and methods of the invention allowthe use of small volumes of blood to monitor platelet activity.Specifically, in some embodiments, less than about 2 ml, less than about1 ml, less than about 0.4 ml, less than about 0.2 ml, less than about0.1 ml, or less than 50 μl is used. In some embodiments, a drop, such asis formed by a finger prick, can be used.

Certain embodiments of the obstruction or irregularity are shown inFIGS. 1A-F. FIG. 1A shows a wire 120 as an obstruction. The wire 120 canbe centered or off-center in the passageway. Either or both of thepassageway 100 and wire 120 can have non-circular cross-sections. Thewire 120 in this embodiment can be replaced with a plug of anynon-porous material. The wire can be any length, and can be shorter thanit is wide.

The obstruction can be multiple wires or plugs 121, as shown in FIG. 1B.

The passageway can comprise an irregularity rather than, or in additionto, an obstruction. The irregularity can be any angle, narrowing,expansion, or curve in the passageway that is suitable to allowformation of a platelet mass. For instance, the irregularity can be step130 in the wall of the passageway, as shown in FIG. 1C. The smallerdiameter section of the passageway could be on the same center as thelarger diameter section, or offset.

The irregularity could be a narrowed section 131 of the passageway, asshown in FIG. 1D. The irregularity could also be an expansion 132 in thepassageway 100 (FIG. 1E).

Another example of a suitable obstruction is an inserted flow restrictor122 (FIG. 1F). The flow restrictor could be, for example, a filtermembrane; a single filter or a plurality of fibers, wires, or ribbons;or a piece of woven or knitted fabric.

A plurality of obstructions or irregularities, or a combination of bothobstructions and irregularities can be used.

The passageway in the invention can be circular, square, or any othershape in cross-section. The passageway can be curved or linear.

Any flow pattern can be used that produces a platelet mass in a suitabletime. For instance, steady unidirectional, or oscillating bidirectionalflow can be used. With oscillating bidirectional flow, the oscillationpattern can be sinusoidal, saw tooth, square wave, asymmetric saw tooth,trapezoidal, asymmetric trapezoidal, or other patterns. Inunidirectional flow, a pulsate component can be superimposed on thesteady flow, and the pulsate component can have any of the abovepatterns. The flow patterns can also vary with time or with measuredresistance to reduce the risk of dislodging a platelet mass once it hasstarted to form. Dwell periods (no flow) can be introduced to allowaggregation of platelets activated by shear.

To achieve the flow patterns described, a pump is preferably used todraw a predetermined volume of blood at a predetermined flow rate(although the flow rate can vary with time, as described above) and apredetermined shear rate into and through the passageway.

An example of a device for monitoring platelet function of the inventionis shown in FIG. 2. A three-way y-shaped flow divider 150 with threeluer locks 180, 181, and 182 at its openings is linked to a tube 140 atluer lock 181 to form the passageway 100. The passageway 100 containswire 120, which is held in position at the open end of the passageway.Blood can be placed in the device by linking a syringe to luer lock 180.Luer lock 182 links the flow divider 150 to a bidirectional pump 160.The bidirectional pump 160 is coupled to a pressure transducer 170 tomonitor the pressure in the passageway. After blood is placed in thepassageway, the opening at luer lock 180 can be closed. Blood is thenpumped back and forth through the passageway until a platelet massforms, slowing or stopping the flow, as detected by the pressuretransducer. The time is recorded as the platelet mass formation time.

One embodiment of an article for use in a device for monitoring plateletfunction is composed of a rigid precision-molded plastic piece, with apassageway molded therein. The article can have an aperture foraccepting blood, linked to the passageway. The ends of the passagewaycan be open to the air to allow free flow of blood without pressurebuildup. The passageway in one embodiment is about a millimeter indiameter and a few cm long, with a stainless steel wire plug of a fewmillimeters length fixed to one wall of the passageway. The gap betweenthe wire plug and the other wall of the passageway can be, for example,about 50 microns. The article can be placed in a flow detection device,where the device includes a bidirectional pump linked to the passagewayand an LED and a coupled detector are placed across one end of thepassageway. The detector detects the passing of blood and then air, asthe blood is pumped back and forth, until a platelet mass forms andprevents the passing of blood. The article can be made of inexpensiveplastic so it is disposable.

One of the advantages of the invention is that no biological or chemicalagent that activates platelets must be added to the blood or to thepassageway through which blood is pumped. Thus, in some embodiments ofthe invention, the passageway (prior to addition of blood) does notcontain an added biological agent that activates platelets. The bloodalso optionally does not contain an added biological agent thatactivates platelets. In some embodiments both the passageway and blooddo not have an added biological agent that activates platelets.

In some embodiments, either or both of the passageway and blood do notcomprise an added chemical agent that activates platelets.

In some embodiments, the passageway does not comprise a biologicalcomponent to which platelets naturally adhere.

In specific embodiments, the passageway does not comprise collagen, ADP,epinephrine, or a derivative thereof.

In some embodiments, no biological or chemical agents are added to theremoved blood. For instance, in some embodiments, no anti-coagulants areadded to the removed blood. In some embodiments, the passageway andblood do not comprise an added anti-coagulant.

However, the methods optionally can also involve use of an added agentthat activates platelets. The agent can be added to the blood after itis removed from the body of the mammal, or it can be added to thepassageway of the device and thus added to the blood as the blood passesthrough the passageway. For instance, the walls of the passageway, orthe walls of an obstruction can be coated with the agent. If theobstruction is a filter, the filter could be soaked in the agent. Amongthe agents that could be used are thromboxane A₂. Aspirin is believed toinhibit platelet function primarily by inhibiting production ofthromboxane A₂, so in some embodiments of testing the effectiveness ofaspirin therapy, it may be useful to add thromboxane A₂ to the blood orpassageway. In particular, it may be useful to compare the platelet massformation time with and without thromboxane A₂ added to the blood orpassageway.

Other agents that can be added to the removed blood or to the passagewayin some embodiments include any of the activators of platelets. Amongthese are ADP, collagen, thrombin, epinephrine, and serotonin. Othercompounds that are not platelet activators but are beneficial to plugformation could also be added. These include fibrinogen, fibrin, and vonWillebrand factor.

The invention can be used to monitor platelet function of patientstreated with ADP inhibitors. Among these drugs are clopidogrel (PLAVIX)and ticlopidine. In the case of patients treated with ADP inhibitors, ifa platelet-activating agent is added to the removed blood or thepassageway, ADP may be useful as the added agent. In particular, it maybe useful to compare the platelet mass formation time with and withoutADP added to the blood or passageway.

The invention can also be used to monitor platelet function of patientstreated with GPIIbIIIa inhibitors. Among the GPIIbIIIIa inhibitors areTirofiban, Eptifibatide, and Abciximab. In the case of patients treatedwith GPIIbIIIa inhibitors, if a platelet-activating agent is added tothe removed blood or the passageway, fibrinogen may be a preferred agentsince it binds to the GPIIbIIIa receptors.

Thus, the invention also provides a method of monitoring plateletfunction comprising: (a) passing blood removed from a mammal through apassageway comprising an obstruction or irregularity to contact theobstruction or the wall of the passageway at the irregularity, togenerate a platelet mass in the passageway; and monitoring the flow orcomposition of the blood in the passageway to determine a platelet massformation time, wherein the blood and passageway do not comprise anadded biological or chemical agent that activates platelets; and (b)passing blood removed from a mammal through a passageway comprising anobstruction or irregularity to contact the obstruction or the wall ofthe passageway at the irregularity, to generate a platelet mass in thepassageway; and monitoring the flow or composition of the blood in thepassageway to determine a platelet mass formation time, wherein theblood and passageway comprise an added biological or chemical agent thatactivates platelets; and (c) comparing the platelet mass formationtimes.

The biological or chemical agent that activates platelets can be, forinstance, thromboxane A₂, ADP, or fibrinogen.

It has been found that the platelet mass formed in some embodiments ofthe invention is substantially free of fibrin and of red and white bloodcells. Thus, in some embodiments, the platelet mass is substantiallydepleted in fibrin in comparison to a natural clot. For instance, theplatelet mass can contain less than about 50%, less than about 30%, lessthan about 10%, or less than about 5% of the fibrin per unit mass foundin a natural clot in the peripheral blood system. In other embodiments,the platelet mass has no detectable fibrin. In certain embodiments, theplatelet mass is substantially depleted in red cells and/or white cells(e.g., contains less than about 50%, less than about 30%, less thanabout 10%, or less than about 5% of the red or white cell found in anatural clot in the peripheral blood stream or has no detectable red orwhite cells).

In some embodiments of the invention the blood passes (e.g., is pumpedpast) the obstruction or irregularity in the passageway.

Platelet mass formation can be detected by monitoring the flow or thecomposition of the blood in the passageway. In some embodiments, theflow is monitored. Flow can be monitored, for instance, by monitoringthe pressure of the blood in the passageway or optically. The pressurecan be monitored with a pressure transducer. Optical monitoring can be,for instance, with a LED and a coupled light detector. The opticalmonitoring, or other methods, can be used to measure the time for bloodto travel a certain distance in the passageway. Flow can also bemonitored by a flow meter or by volume displacement, as well as by othermeans known to those of skill in the art.

In some embodiments, the composition of the blood in the passageway ismonitored. For instance, formation or size of the platelet mass can bedirectly monitored, e.g., by optical means such as with an LED or aspectrophotometer. The chemical composition of the blood can also bemonitored. For instance, pH or concentration of O₂, CO₂, Mg⁺⁺, or K⁺ canbe monitored, as these correlate with platelet mass formation.

In some embodiments, the passageway comprises an obstruction. Theobstruction can be, for instance, a plug. The plug can be a metal wire,plastic, ceramic, glass, or any non-porous substance. The plug can fullyor partially obstruct the passageway.

In some embodiments the platelet mass develops thickness in alldimensions. That is, these embodiments of the methods require plateletaggregation in addition to platelet adhesion. Thus, in some embodiments,the platelet mass has a thickness in all dimensions of at least about 20microns, at least about 30 microns, at least about 40 microns, at leastabout 50 microns, at least about 70 microns, or at least about 100microns.

In some embodiments of the invention, the passageway does not comprise abiological component to which platelets naturally adhere.

In some embodiments, the passageway does not comprise collagen, ADP,epinephrine, or a derivative thereof.

In some embodiments, the passageway and blood do not comprise an addedanti-coagulant.

In some embodiments of the methods, the method further comprises addinga platelet activator to the blood. In some embodiments the passagewaycomprises a platelet activator. The platelet activator can be, forinstance, thromboxane A₂.

In some embodiments of the methods and devices of the invention, theplatelets are activated at least partially by mechanical forces. In someembodiments, the platelets are activated solely by mechanical forces. Itis believed that the platelets in the methods of the invention areactivated by high shear and adhere at a point of low shear. However, byvarying the dimensions of the passageway, the velocity of flow generatedby the blood pumping, and the material of the walls of the passagewayand of any obstructions (e.g., the adhesiveness of the material), wideranges of shear can be used. Maximum shear rates in different devices inwhich platelet mass formation was detected spanned at least the range of50 to 5,000 sec⁻¹.

In some embodiments, less than 2 ml, less than 1 ml, less than 0.4 ml,less than 0.2 ml, less than 0.1 ml, or less than 50 μl of blood isremoved from the body of the mammal. In some embodiments, less thanthese amounts are transferred to the passageway.

In some embodiments of the invention, the blood passes bidirectionallythrough the passageway. In other embodiments, at least part of thepassageway is a loop (i.e., a closed circuit, whether circular, oval,square, or another shape) and the blood passes unidirectionally throughthe loop.

In some embodiments of the invention, the blood is whole blood. In someembodiments, the removed blood is fractionated before being used in themethods and devices of the invention.

In some embodiments of the devices and articles of the invention, thedevice or article further comprises a fluid-tight material forming anaperture linked to the passageway.

In some embodiments of the devices of the invention, the device operateswithout a biological agent that activates platelets. In someembodiments, the device operates without a chemical agent that activatesplatelets.

In some embodiments of the devices and articles of the invention, theobstruction in the passageway is arranged such that when blood is pumpedthrough the passageway to contact the obstruction, a platelet mass thatis substantially free of fibrin and is at least about 20 micron thick inall dimensions forms on or near the obstruction.

In some embodiments of the devices and articles of the invention, theirregularity in the passageway is arranged such that when blood ispumped through the passageway to contact the wall of the passageway atthe irregularity, a platelet mass that is substantially free of fibrinand that is at least about 20 micron thick in all dimensions forms onthe wall of the passageway at or near the irregularity.

In some embodiments, the blood flows past the obstruction orirregularity, and the obstruction or irregularity leaves a passageway atleast 20 microns in diameter or width at the obstruction orirregularity. For instance, the gap between a plug and the wall of thepassageway is at least 20 microns in these embodiments. For anotherexample, the diameter or width of the passageway at the narrowest pointof the passageway at an irregularity that narrows the passageway is atleast 20 microns in these embodiments. When a platelet plug forms thatfills the passageway at this point, the passageway is occluded and thisis detected as a change in the flow of the blood in the passageway.Thus, the method detects the formation of a platelet plug at least 20microns thick. In other embodiments, the obstruction or irregularityleaves a passageway of at least 50 microns, at least 100 microns, 20 to100 microns, or 20 to 200 microns in diameter or width at theobstruction or irregularity.

In some embodiments of the invention, the mammal whose platelet functionis monitored is treated with an anti-platelet agent. In particularembodiments, the anti-platelet agent comprises a cyclooxygenaseinhibitor (e.g., aspirin or other salicylates), an ADP inhibitor, aGPIIbIIIa inhibitor, or a combination thereof.

Several uses of the methods and devices of the invention exist. Themethods and devices can be used to monitor the effectiveness ofanti-platelet agents in patients treated with anti-platelet agents. Suchpatients include those treated by interventional cardiologycatheterization. This includes angiograms, angioplasty, and stentplacement. In addition, the methods can be used to monitor theeffectiveness of anti-platelet agents in patients who receive anartificial heart valve.

The methods and devices can be used to monitor the effectiveness ofaspirin or other anti-platelet agents in patients taking the agents toprevent a cardiovascular event, such as coronary thrombosis (heartattack), pulmonary embolism, stroke, or deep vein thrombosis due toexcessive platelet activity.

The methods and devices can be used to test patients for their risk ofexcessive bleeding. This testing can be needed, for instance, prior to asurgical or dental procedure. For instance, the methods can be used onpatients prior to having a tooth pulled or wisdom tooth removed todetermine their risk of excessive bleeding. If it is determined that thepatient is at risk of excessive bleeding, appropriate precautions can betaken, such as doing the procedure in a setting where a bloodtransfusion or platelet transfusion is available.

The methods can also be used to monitor liver function. When liverfunction falls, blood flow through the spleen increases. The spleen,which normally degrades old non-functional platelets, then begins todegrade good platelets as well and the platelet count falls. Since afall in platelet function can be due to low platelet count, by detectinglow platelet function the present methods provide a quick way ofdetecting possible low platelet count. Accordingly, they can be used toscreen for liver disease including hepatitis A, B, and C, cirrhosis, andliver damage due to alcoholism.

The invention will now be illustrated by the following non-limitingexamples.

EXAMPLES Example 1 Characterization of Platelet Mass Adhering to Wire ina Tube

Methods:

Platelet mass formation. Human blood was pumped through the lumen of aTEFLON tube with a 24 gauge stainless steel wire in the lumen of thetube, the wire being held in place at the end of the tube. Twentymicroliters of blood was pumped in a cycle of 35 seconds at a flow rateof 20/35=1.75 microliters per second. The flow corresponded to a peakshear rate of 1600 sec⁻¹. Following formation of the platelet mass onthe end of the wire, the wire and attached platelet mass were rinsed in0.9% PBS for 5 minutes, then fixed in 1% glutaraldehyde for 3 hours.

Antibody staining. The fluorescein-conjugated monoclonal antibody CD45(Becton Dickinson) is specific for the surface receptor GPIb, which isfound on platelets and not on other blood cells. Ten microliters of thefluorescent antibody was added to the mass on the tip of the wire andincubated in the dark at room temperature for 30 minutes.Non-specifically bound monoclonal antibody was removed from the samplewith five 5-minute washes with 0.9% PBS. Fluorescent microscopy was thenperformed.

Electron microscopy. In another experiment, the mass attached at the endof the wire and fixed with glutaraldehyde was characterized bytransmission electron microscopy. The wire and mass were mounted inembedding solution, and cross-sections of the mass were cut usingstandard sectioning procedures. The cross-sections were evaluated bytransmission electron microscopy.

Results:

Fluorescent microscopy showed uniform staining of the mass on the end ofthe wire with the platelet-specific antibody, with deeper color atpoints where the mass was deeper. (Data not shown.) This shows the massconsisted largely of platelets, and that platelets were uniformlydistributed in the mass.

Electron microscopy showed that the mass consisted only of smallanucleated cells (i.e., platelets). No cells containing nuclei (i.e.,white blood cells) were seen. In addition, no larger anucleated cells(red blood cells) were identified. Additionally, no fibrin strands werevisible in the samples viewed by transmission electron microscopy. Thus,the mass produced by this device on the end of the wire was a plateletmass that was free of fibrin and appeared to be free of other bloodcells.

Example 2 Monitoring Platelet Activity in Pigs Receiving Aspirin

Methods:

Pigs were placed on various platelet inhibitors and then the plateletfunction of the pigs was monitored. Twenty-five pigs received 300 mgaspirin daily for seven days. Ten pigs received 300 mg ticlopidine (anADP inhibitor) daily. Ten pigs received a combination of 300 mg aspirinand 300 mg ticlopidine daily.

Arterial blood was drawn and placed in a device similar to the deviceshown in FIG. 2. Twenty microliters of blood were drawn into the lumenof the tube at a rate of 1.0 microliter per second. The wire was 0.016inches in diameter and the inner diameter of the tube was 0.034 inchesin diameter. Blood (20 μl) was delivered via a three-way flow divider (aTouhy-Borst Connector) into a TEFLON tube 2 inches long with a stainlesssteel wire 0.16 inches in diameter inserted through the tube andextending about three-fourths of the length of the tube. The wire washeld in place at the end of the tube. The tube was coupled to a Hamiltonsyringe pump and to a HP blood pressure transducer for measuring thepressure in the tube. The platelet plug formation time was determined asdamping of the blood pressure signal.

Results:

The results are shown in Tables 1-3 below. TABLE 1 Platelet plugformation time of pigs receiving aspirin. Day Mean platelet plug time(minutes) Before aspirin 3.25 (±0.35)  After 3 days 3.9 (±0.25) After 7days 4.6 (±0.42)

TABLE 2 Platelet plug formation time of pigs receiving ticlopidine. DayMean platelet plug time (minutes) Before ticlopidine 3.31 After 3 days5.67 After 7 days 6.21

TABLE 3 Platelet plug formation time of pigs receiving aspirin andticlopidine. Day Mean platelet plug time (minutes) Before treatment 2.6After 1 day 2.6 After 3 days 2.6 After 7 days 18.5

The results show that the method used allowed detection of a change inplatelet function in the pigs in response to both aspirin (acyclooxygenase inhibitor) and ticlopidine (an ADP inhibitor). Thus, themethod successfully monitors response to anti-platelet drugs, and is notspecific for a particular type of anti-platelet drug.

All patents, patent documents, and references cited are incorporated byreference.

1. A method for monitoring the flow or composition of blood comprising:passing whole blood removed from a mammal through a passagewaycomprising an obstruction in the passageway and a narrowing of thepassageway; contacting the blood with the obstruction and the narrowing;and monitoring the flow or composition of the blood in the passageway,wherein the blood passes bidirectionally through the passageway; andwherein less than 2 ml of blood is removed from the body of the mammal.2. The method of claim 1, wherein less than 1 ml of blood is removedfrom the body of the mammal.
 3. The method of claim 1, wherein less than0.4 ml of blood is removed from the body of the mammal.
 4. The method ofclaim 1, wherein less than 0.2 ml of blood is removed from the body ofthe mammal.
 5. The method of claim 1, wherein less than 0.1 ml of bloodis removed from the body of the mammal.
 6. The method of claim 1,wherein less than 50 μl of blood is removed from the body of the mammal.7. The method of claim 6, wherein the blood is removed from the body ofthe mammal by a finger prick.
 8. The method of claim 1, wherein a singledrop of blood is removed from the body of the mammal.
 9. The method ofclaim 8, wherein the blood is removed from the body of the mammal by afinger prick.
 10. The method of claim 1, wherein the flow of the bloodin the passageway is monitored.
 11. The method of claim 10, wherein theflow is monitored by monitoring the pressure of the blood in thepassageway.
 12. The method of claim 11, wherein the pressure ismonitored with a pressure transducer.
 13. The method of claim 10,wherein the flow is monitored optically.
 14. The method of claim 13,wherein the flow is monitored with a light-emitting diode and a lightdetector.
 15. The method of claim 1, wherein the composition of theblood in the passageway is monitored.
 16. The method of claim 15,wherein the size of the platelet mass is directly monitored.
 17. Themethod of claim 15, wherein the chemical composition of the blood ismonitored.
 18. The method of claim 17, wherein at least one of the pH,concentration of O₂, concentration of CO₂ concentration of Mg⁺⁺, orconcentration of K⁺ is monitored.
 19. The method of claim 1, wherein theobstruction is one or more plugs that partially obstruct the passageway.20. The method of claim 1, wherein no biological or chemical agents areadded to the removed blood.
 21. The method of claim 1, wherein thepassageway and blood do not comprise an added anti-coagulant.
 22. Themethod of claim 1, wherein the obstruction is a wire.
 23. The method ofclaim 1, wherein the obstruction is a filter.
 24. The method of claim 1,wherein the obstruction is a mesh.
 25. The method of claim 1, whereinthe obstruction is a fiber.
 26. The method of claim 1, wherein theobstruction is a filter membrane.
 27. The method of claim 1, wherein theobstruction is a plurality of fibers.
 28. The method of claim 1, whereinthe obstruction is a plurality of wires.
 29. The method of claim 1,wherein the obstruction is a plurality of ribbons.
 30. The method ofclaim 1, wherein the obstruction is a piece of woven or knitted fabric.31. A device for monitoring the flow or composition of blood comprising:a fluid-tight material forming a passageway comprising an obstruction inthe passageway and a narrowing of the passageway; a pump functionallylinked to the passageway for pumping blood through the passageway; and adetector for detecting the flow or composition of blood in thepassageway, wherein the obstruction and the narrowing are arranged suchthat when blood is pumped through the passageway, the blood contacts theobstruction and the narrowing.
 32. The device of claim 31, wherein thedetector detects the flow of blood in the passageway.
 33. The device ofclaim 31, wherein the detector detects the composition of blood in thepassageway.
 34. The device of claim 31, wherein the pump is capable ofpumping blood through the passageway bidirectionally.
 35. The device ofclaim 31, wherein the obstruction and the narrowing are arranged suchthat when blood is pumped through the passageway, the blood contacts theobstruction and the narrowing and generates a platelet mass in thepassageway.
 36. The device of claim 35, wherein the platelet mass issubstantially depleted in fibrin in comparison to a natural clot. 37.The device of claim 31, wherein the passageway has a volume of less than2 ml.
 38. The device of claim 31, wherein the passageway has a volume ofless than 1 ml.
 39. The device of claim 31, wherein the passageway has avolume of less than 0.4 ml.
 40. The device of claim 31, wherein thepassageway has a volume of less than 0.2 ml.
 41. The device of claim 31,wherein the passageway has a volume of less than 0.1 ml.
 42. The deviceof claim 31, wherein the passageway has a volume of less than 50 μl ml.43. The device of claim 32, wherein the flow of blood in the passagewayis detected by monitoring the pressure of the blood in the passageway.44. The device of claim 43, wherein the device further comprises apressure transducer.
 45. The device of claim 33, wherein the compositionof blood in the passageway is detected by monitoring at least one of thepH, concentration of O₂ concentration of CO₂, concentration of Mg⁺⁺, orconcentration of K⁺.
 46. The device of claim 31, wherein the obstructionis one or more plugs that partially obstruct the passageway.
 47. Thedevice of claim 31, wherein the obstruction is a wire.
 48. The device ofclaim 31, wherein the obstruction is a filter.
 49. The device of claim31, wherein the obstruction is a mesh.
 50. The device of claim 31,wherein the obstruction is a fiber.
 51. The device of claim 31, whereinthe obstruction is a filter membrane.
 52. The device of claim 31,wherein the obstruction is a plurality of fibers.
 53. The device ofclaim 31, wherein the obstruction is a plurality of wires.
 54. Thedevice of claim 31, wherein the obstruction is a plurality of ribbons.55. The device of claim 31, wherein the obstruction is a piece of wovenor knitted fabric.
 56. The device of claim 31, wherein the deviceoperates without a biological or chemical agent that activatesplatelets.
 57. The device of claim 31, wherein the device operateswithout an anti-coagulant.
 58. A method of monitoring the plateletfunction of whole blood comprising: passing whole blood removed from amammal through a passageway comprising an obstruction or anirregularity; contacting the blood with the obstruction or the wall ofthe passageway at the irregularity to generate a platelet mass in thepassageway; and monitoring the flow or composition of the blood in thepassageway to detect formation of the platelet mass; and determiningfrom the monitoring a measure of the platelet function of the blood,wherein the platelet mass is substantially depleted in fibrin incomparison to a natural clot; wherein the blood passes bidirectionallythrough the passageway; and wherein less than 2 ml of blood is removedfrom the body of the mammal.
 59. The method of claim 58, wherein lessthan 1 ml of blood is removed from the body of the mammal.
 60. Themethod of claim 58, wherein less than 0.4 ml of blood is removed fromthe body of the mammal.
 61. The method of claim 58, wherein less than0.2 ml of blood is removed from the body of the mammal.
 62. The methodof claim 58, wherein less than 0.1 ml of blood is removed from the bodyof the mammal.
 63. The method of claim 58, wherein less than 50 μl ofblood is removed from the body of the mammal.
 64. The method of claim63, wherein the blood is removed from the body of the mammal by a fingerprick.
 65. The method of claim 58, wherein a single drop of blood isremoved from the body of the mammal.
 66. The method of claim 65, whereinthe blood is removed from the body of the mammal by a finger prick. 67.The method of claim 58, wherein the flow of the blood in the passagewayis monitored.
 68. The method of claim 67, wherein the flow is monitoredby monitoring the pressure of the blood in the passageway.
 69. Themethod of claim 68, wherein the pressure is monitored with a pressuretransducer.
 70. The method of claim 67, wherein the flow is monitoredoptically.
 71. The method of claim 70, wherein the flow is monitoredwith a light-emitting diode and a light detector.
 72. The method ofclaim 58, wherein the composition of the blood in the passageway ismonitored.
 73. The method of claim 72, wherein the size of the plateletmass is directly monitored.
 74. The method of claim 72, wherein thechemical composition of the blood is monitored.
 75. The method of claim74, wherein at least one of the pH, concentration of O₂, concentrationof CO₂ concentration of Mg⁺⁺, or concentration of K⁺ is monitored. 76.The method of claim 58, wherein the passageway comprises an obstruction.77. The method of claim 76, wherein the obstruction is one or more plugsthat partially obstruct the passageway.
 78. The method of claim 58,wherein the platelet mass has a thickness in all dimensions of at leastabout 20 microns.
 79. The method of claim 58, wherein the platelets areactivated at least partially by mechanical forces.
 80. The method ofclaim 79, wherein the platelets are activated solely by mechanicalforces.
 81. The method of claim 58, wherein the platelet mass issubstantially depleted in red blood cells and white blood cells incomparison to a natural clot.
 82. The method of claim 58, wherein thepassageway does not comprise an added biological agent that activatesplatelets.
 83. The method of claim 58, wherein the blood does notcomprise an added biological agent that activates platelets.
 84. Themethod of claim 58, wherein the passageway and blood do not comprise anadded chemical agent that activates platelets.
 85. The method of claim58, wherein no biological or chemical agents are added to the removedblood.
 86. The method of claim 58, wherein the passageway does notcomprise a biological component to which platelets naturally adhere. 87.The method of claim 58, wherein the passageway does not comprisecollagen, ADP, epinephrine, or a derivative thereof.
 88. The method ofclaim 58, wherein the passageway and blood do not comprise an addedanti-coagulant.
 89. The method of claim 58, further comprising adding aplatelet activator to the blood.
 90. The method of claim 58, wherein thepassageway comprises a platelet activator.
 91. The method of claim 89,wherein the platelet activator is thromboxane A₂.
 92. The method ofclaim 90, wherein the platelet activator is thromboxane A₂.
 93. Themethod of claim 58, wherein the mammal is treated with an anti-plateletagent.
 94. The method of claim 93, wherein the anti-platelet agentcomprises a cyclooxygenase inhibitor, an ADP inhibitor, a GPIIbIIIainhibitor, or a combination thereof.
 95. The method of claim 58, whereinthe passageway comprises an obstruction.
 96. The method of claim 95,wherein the obstruction is a wire.
 97. The method of claim 95, whereinthe obstruction is a filter.
 98. The method of claim 95, wherein theobstruction is a mesh.
 99. The method of claim 95, wherein theobstruction is a fiber.
 100. The method of claim 95, wherein theobstruction is a filter membrane.
 101. The method of claim 95, whereinthe obstruction is a plurality of fibers.
 102. The method of claim 95,wherein the obstruction is a plurality of wires.
 103. The method ofclaim 95, wherein the obstruction is a plurality of ribbons.
 104. Themethod of claim 95, wherein the obstruction is a piece of woven orknitted fabric.
 105. The method of claim 58, wherein the passagewaycomprises an irregularity.
 106. The method of claim 105, wherein theirregularity is a narrowing of the passageway.
 107. The method of claim105, wherein the irregularity is a widening of the passageway.